"Florida Democrats ran the strongest, largest ground game this state has ever seen," he said, describing it as "appalling" that the state had been unable to report results two days after the election.

Republican officials also said they expected Mr Obama to eventually be declared the winner.

"We thought based on our polling and range of organisation that we had done what we needed to win," Brett Doster, a Florida adviser for Mr Romney, told the Miami Herald.

"Obviously, we didn't, and for that I and every other operative in Florida has a sick feeling that we left something on the table. I can assure you this won't happen again."

Florida Republican spokesman Brian Burgess told the Associated Press that "given the wave that we saw all over the country, we're glad that we gave them enough of a fight in Florida to prolong the battle here as long as we did".

Obama campaign manager Jim Messina told reporters: "We feel we will be the official winner in Florida later today."

Counties must send preliminary results to the state by midday on Saturday.

Voting problems

Long queues were reported across the fourth most populous US state on Tuesday.

Some voters waited to cast ballots until 01:30 local time the next morning, after Mr Romney had already delivered his concession speech.

Tens of thousands of absentee ballots also arrived on election day.

In Broward County, Democratic Mayor John Rodstrom told the Miami Herald: "The big picture is that we have done this to ourselves," blaming a combination of all sorts of municipal, state and federal elections on one ballot.